In order to prolong the life of molten carbonate fuel cells, the amount of electyrolyte in the matrix must be maintained at an appropriate level over long-term operation. Lithium aluminate, the state-of-the-art material for the matrix substrate, still presents some problems, such as crystal phase stability and particle growth. The mechanism of phase transformation and particle growth of lithium aluminate under various conditions (temperature, gas composition, carbonate composition) are investigated. Moreover, the effect of several additives for inhibiting particle growth are investigated. It is found that the allotropic phase transformation and particle growth occurs via a ＇dissolution-deposition＇ mechanism. The results obtained suggest that lower temperature, higher partial pressure of CO2 or lower basicity of carbonates are preferable to control the particle growth of lithium aluminate and that alpha-lithium aluminate appears more stable under typical MCFC operating conditions. Potassium tungstate inhibits the particle growth of the lithium aluminate containing beta-phase.